1. Technical Field of the Invention
This invention relates generally to thermal solutions for semiconductor packaging, and more specifically to thermal solutions using a vapor chamber such as in heatpipes.
2. Background Art
Semiconductor packages presently rely upon a primarily conductive model for transmitting heat from the surface of the semiconductor die to the exterior of the package. This model includes a number of interfaces, each of which drives an increase in the thermal resistance of the package.
FIG. 1 illustrates a generalized semiconductor packaging system 10 such as is known in the prior art. The system includes a package having a package bottom 12 and a package top 14 or integrated heat spreader which encompass a cavity 16 within which a semiconductor die 18 is contained. The semiconductor die is electrically connected through the package bottom to a number of pins or contacts 22 on the exterior of the packaging system. The semiconductor die is thermally interfaced to the package top with a quantity of a first thermal interface material 24 which improves thermal transfer from the die to the interior surface of the package top. The exterior surface of the package top is thermally coupled to a heatsink 26 with a quantity of a second thermal interface material (TIM) 28. The reader will appreciate that this is a generalized and simplified view of the packaging system, for purposes of discussion.
Table 1 lists exemplary typical ratios of the various components of the aggregate thermal resistance of the system. Thermal resistance is measured in degrees Celsius per watt from the junction of the semiconductor device to the ambient air, in the case of an air-cooled system.
In order to achieve good thermal contact across the second thermal interface layer 28, the heatsink is mechanically fastened to the package or to the computer chassis or motherboard (not shown), with strong springs or with bolts. This creates a large force (shown as Fn in FIG. 1) which is normal to the mating surfaces of the heatsink and the package top. This force is necessary to ensure a thin layer of TIM2 material with optimal thermal characteristics. However, this force can cause electrical and/or mechanical breakdown of the die, the package, connection to the package contacts, and so forth.
FIG. 2 illustrates a generalized, simplified heatpipe system 30 as is known in the prior art. The system includes a heatpipe 32 coupled to conduct heat from a hot device 34 to a cooling device 36. The body of the heatpipe encloses a vapor chamber 38 which contains a quantity of a working fluid 40 which does not completely fill the vapor chamber. The vapor chamber may also include a wicking material 42, which improves performance in configurations or orientations in which the working fluid is not held by gravity against the hot device end of the vapor chamber. As the hot device boils the working fluid, the working fluid vaporizes. As the vapor condenses elsewhere in the heatpipe nearer the cooling device, the significant amount of heat captured by the phase change is released, effecting an efficient thermal transfer from the hot end of the heatpipe to the cooler end. Any suitable cooling fluid can be used, such as water, alcohol, flourinert, or the like. Any suitable active or passive cooling device can be used, such as a heatsink, heat spreader, peltier device, refrigerator coil, or the like.